Na-K-ATPase plays a key role in the ionic homeostatis of most mammalian cells. In most cells this pump has been demonstrated to translocate 3Na+ out of the cell and 2K+ into the cell for every ATP hydrolyzed. The energetics of Na-K-ATPase in cultured cell lines is being investigated in this study to establish the relative amount of energy used by the enzyme in cultured cells and investigate the metabolic pathways through which energy is supplied to this active ion pump. We have established that the efficiency of Na-K-ATPase (i.e. the amount of K+ pumped per ATP hydrolized) is the same (2K/ATP) as in normal freshly isolated tissue. We have established that glycolysis is the preferred pathway for providing ATP to Na-K-ATPase eventhough glycolysis only provides 30% of the total ATP production by the cell. The reason for this phenomenon is still being investigated.